Atmospheric ice-particles may pose a threat for engines of aircraft in flight. Ice-particles may get into aircraft engines and attach themselves to engine surfaces, building up until ice causes engine failure in some way. The ice particles typically are present in the atmosphere in the form of ice-particle aerosols.
Aircraft born radar systems are known for detecting atmospheric phenomena, such as clouds, rainfall, and Clear Air Turbulence (CAT). Ice crystals often exist in optically dense clouds at high-altitude. Radar systems, however, use electromagnetic radiation (EMR) wavelengths of a few meters to a few mm in wavelength, which are much larger than the size of ice-particles in typical atmospheric ice-particle aerosols of ˜10 microns to 1000 microns. In this case, ice-particle aerosols comprise particles far too small to provide significant backscatter returns for Radar systems, because the scattering cross sections are very small.
Lidar (light detection and ranging) systems are known to have been used for detecting ice-crystals in clouds. The amplitude of lidar returns from clouds can be large, with potentially high signal-to-noise ratios being possible. Lidar instrumentation, however, is typically physically large (the optics have a characteristic diameter of 30 cm-50 cm), heavy, costly, fragile and power-hungry, and thus is not used for airplane deployment.